Biolab follows protocols for breath hydrogen and methane testing that are in line with current practice in Europe and America [1,2].

Normally the human small intestine contains fewer bacteria than the colon. Structural or functional disorders of the gastrointestinal tract can lead to bacterial overgrowth in the small intestine, with colonic bacteria proliferating in the ileum and jejunum. Small intestinal bacterial overgrowth (SIBO), as it is known, is characterized by steatorrhea and diarrhoea, together with vitamin deficiencies and carbohydrate malabsorption. The syndrome is difficult to diagnose with accuracy using blood tests.

The basis for breath testing in these circumstances is that bacteria in the intestine can break down carbohydrates to produce hydrogen and methane. The sole source of these gases in alveolar air is bacterial fermentation of carbohydrate in the gut, so estimation of hydrogen and methane in breath samples can be used to study the passage of carbohydrates through the gut and the presence of pathogenic bacteria in the gastro-intestinal lumen.

Breath tests can be helpful in the evaluation of bloating, diarrhoea, constipation and malabsorption. These tests are safe alternatives to more invasive procedures such as biopsy. According to research from the 1970s, which was repeated in 2006 [3], approximately 35% of healthy adult subjects are methane producers. It was also reported [4] that, in 34% of lactose intolerant patients with a negative hydrogen breath test, the methane percentage increase after a lactose challenge was greater than 100%. In the same study, out of 13 subjects with a false negative breath hydrogen response to lactulose, 11 subjects had a methane percentage increase greater than 100%. Methanogenic bacteria are independent of hydrogen-producing bacteria; so methane determination along with the measurement of hydrogen is thus required in the study of lactose intolerance [5] and in other carbohydrate breath tests.

Breath testing to aid in the diagnosis of small intestinal bacterial overgrowth (SIBO) may also provide a framework for the understanding of irritable bowel syndrome (IBS) [6,7]. Recent work has demonstrated that among IBS subjects, methane production in the lactulose breath test is associated with constipation. Methane also appears to slow down the passage of food through the intestinal tract [8].

Patient Instructions:

The patient should not have eaten slowly digesting foods such as beans and bran on the day before the test and should have fasted for 14 hours prior to the test, with only water to drink. Vigorous exercise, smoking or sleeping should be avoided immediately before, or at any time during the test.

Appointment Notes:

The test will take 3 hours.

Home test kits are also available on request (payment required in advance).

Clinical Indications:

Normally there is a peak in hydrogen production two hours after lactulose ingestion, reflecting the passage of this non-absorbable carbohydrate into the colon. With increased intestinal transit time, the appearance of the hydrogen peak may be delayed, as often occurs where there is significant methane production. In small intestinal bacterial overgrowth (SIBO) there is also an earlier peak of hydrogen production, reflecting the breakdown of lactulose in the jejunum and ileum. Some subjects produce little or no hydrogen, but display a substantial output of methane, due to the particular metabolism of the species of bacteria proliferating in their gut.

A lactulose breath test for small SIBO is thus positive if there is a biphasic pattern of breath hydrogen or methane production. Two peaks of gas production are observed in a positive test:a) an early increase of at least 20 ppm for the sum of the concentration of the two gases, b) a larger increase (greater than 20 ppm) corresponding to the appearance of lactulose in the colon.In cases of fast intestinal transit time the two peaks may merge as an early plateau of gas production.

In a negative lactulose test only the colonic peak in gas production is observed and there is no significant increment in gas production prior to 120 minutes post lactulose ingestion. The absence of normal colonic bacterial fermentation suggests that the patient has recently used antibiotics.

The lactulose breath test can also detect impaired intestinal transit time; transit time is normal if the physiological peak of colonic hydrogen and methane production (>20 ppm) is detected at 80 minutes, slow if the peak is detected at 100 minutes or later, or fast if the peak is detected at 60 minutes or earlier. Note that the presence of lactulose increases intestinal motility, so these times are not typical of the transit time of a normal meal.

In subjects who do not absorb lactose (a disaccharide which is normally broken down into glucose and galactose and then absorbed) there is abnormally high production of hydrogen and perhaps methane as this carbohydrate passes into the lower small intestine. A lactose breath test is positive if either the hydrogen peaks by >20 ppm compared to the basal sample or if the methane peaks by >12 ppm compared to the basal sample .

In subjects who do not absorb fructose (a monosaccharide normally present in food) there is high production of hydrogen and perhaps methane as this carbohydrate passes into the lower gut. A fructose breath test is positive if either the hydrogen peaks by >20 ppm compared to the basal sample or if the methane peaks by >12 ppm compared to the basal sample.

For the lactulose breath test the patient is given 10 gm of lactulose syrup with 200 ml of water; alveolar air samples are collected at baseline and then every 20 minutes for 3 hours (a total of 10 samples). If the result is equivocal, it is recommended that the test should be repeated using 40 gm of lactulose.Home collection breath tubnes stable for at least 14 days after collection